Samples Preparation Method

Because N can volatilize from samples dried above 60°C, samples analyzed for %C and %N should be dried at 55oC. Soil should be sieved through a 2 mm mesh to remove roots and gravel. Plant and soil samples must be ground to the consistency of cocoa powder. Special care must be taken to keep samples completely free of moisture after they are ground through being weighed, otherwise moisture will be considered part of the sample weight and will result in unrepresentative percent C and N. Ground and dry samples are weighed into tin capsules using a microbalance (50-70 mg for soils with <10% C, 20-30 mg for more organic soil, and 5-10 mg for plant tissue), recorded to 0.001 mg, and stored in a desiccator until analysis. Please contact the SASC manager for information and training on sample preparation.

    Sample Preparation Procedures

    Preparing soil samples for Total Carbon and Nitrogen analysis using an Elemental Analyzer:

    1. Dry 20 g of homogenized soil sample at 55°C for one week.
    2. Pass dried soil through a 2mm sieve.
    3. Place the dried and sieved sample in a large coin envelope labeled in pencil with the researcher's initials and sample ID.
    4. Grind soil samples using a ball-mill grinder for 1-3 minutes.
    5. Put ground soil samples in coin envelop and dry for >1 day at 55°C
    6. Transfer dried samples to the CN sample desiccator.
    7. Weigh ~ 50.000-60.000 mg of soil into tin capsules using a microbalance (20-30 mg for more organic soil). 
    8. Fold the tin capsule to eliminate air in the sample, forming a square so the sample does not roll.
    9. Enter weights and sample IDs into the spreadsheet.

    Preparing soil samples for organic carbon analysis using an Elemental Analyzer:

    1. Dry 20 grams of homogenized soil at 55°C for one week.
    2. Pass the dried soil through a 2mm sieve.
    3. Place the dried and sieved soil in a coin envelope labeled in pencil with the researcher's initials and sample ID.
    4. Grind the soil using a ball-mill grinder for 1-3 minutes.
    5. Put the ground soil into the coin envelope and re-dry for over a week at 55°C.
    6. Transfer the dried samples to a desiccator to store them in a dry environment until ready for weighing and further processing.
    7. Using a microbalance, weigh approximately 30.000-40.000 mg of soil into silver capsules. Record the weight in three decimals (i.e., 0.000mg), leave the capsule open, and place it in a well-plate.
    8. Add 0.2-0.3 ml of 1:1 12M HCl to the silver capsule.
    9. Move the well-plate to an oven and dry it at 65°C for two weeks.
    10. Fold and seal the silver capsule tightly. Before folding, consider placing a tin capsule around the silver one to prevent breakage.

    Note: To measure inorganic carbon, a separate sample must be analyzed for total carbon to determine the inorganic carbon content.

      Plant Tissue Processing Procedures

      1. Dry plant material at 55°C for one week.
      2. Homogenize plant material through a Wiley mill and subsample plant material if necessary.
      3. Grind soil samples using a ball-mill grinder if there is adequate sample, otherwise a mortar and pestle must be used
      4. Dry plant samples in labelled coin envelops at 55°C
      5. Store dried samples in desiccator
      6. Weigh ~ 5.000-10.000 mg of plant material into tin capsules using microbalance
      7. Enter weights and sample IDs into spreadsheet